Photoshop edits not saved in iPhoto

I've set up Photoshop CS4 as my external editor in iPhoto, and this has been working well for quite a while. I usually edit in Photoshop and save over the original (both jpeg files) in iPhoto. However, today I noticed that my edited work was not showing up in the gallery view (i.e. even after saving over, the original version of the photo was shown in my gallery). On close-up I can view the edited photo, but once I edit another photo the previous photo I edited reverts to its original form. I've tried repairing the library and permissions by pressing option + command on startup, but the problem still remains. None of my edited work is saved once I close and reopen iPhoto. Please help! :-(